Generator stator slot wedge system that can be adjusted in situ to provide increased radial load

ABSTRACT

A generator stator including a magnetic core having a plurality of axially extending radial slots arranged about the periphery thereof with windings in each radial slot; at least one adjustable assembly axially inboard of an outermost end assembly in each radial slot, arranged to restrain the windings in the radial slot, the adjustable assembly comprising mating wedge and slide components which interface along stepped matching surfaces, the wedge component having an elongated slot therein providing access to the slide component. A tool is provided and includes a tool head pivotally secured to a handle. The tool head is formed with a stub adapted to seat in a hole in the slide component via the slot.

BACKGROUND OF THE INVENTION

[0001] This invention relates to generator stators and, morespecifically, to a wedge and slide system that can be used internally ofthe end wedge and permits in situ radial correction for radial pressureand dimension losses which occur over time.

[0002] Electric utility companies require large turbine-generators tooperate reliably for long periods of time, for example, thirty years ormore. Normal, steady-state electromagnetic forces acting on the armaturewinding are capable of causing armature bar vibration within a muchshorter period than the expected generator lifetime. Armature barvibration can occur if radial clearances are present within the statorcore slot. Bar vibration can result in armature bar insulation abrasion.The abrasion can become severe if maintenance actions are not taken toretighten the slot support system and arrest the vibration. Typically, aprolonged maintenance outage is required to retighten the slot supportsystem and eliminate radial clearances within the slot.

[0003] The electrical windings within the ends of the stator core slotsmay become susceptible to accelerated abrasion due to: 1) pre-existingor rapidly-evolving radial clearances, 2) the effects of excessive orcontinuous oil contamination, and 3) abnormally high electromagneticdesign forces on the slot portion of the winding. It is thereforeimportant to provide an in situ means for eliminating radial clearancesthat develop in this location in order to prevent unscheduled orprolonged service outages.

[0004] In an attempt to address at least some of these problems, astepped wedge and slide arrangement is proposed in U.S. Pat. No.4,149,101 but for the purpose of preventing axial displacement of wedgeswithin the core slot. A stepped bracing arrangement is proposed in U.S.Pat. No. 3,842,303 but in the context of an end winding support fit-updevice between the coil end arms.

[0005] A stepped dovetail wedge and slide system which permitsretightening of the generator stator end slot wedges so as to restorethe required radial force on the winding bars is disclosed in copendingapplication Ser. No. (not known) (atty. dkt. 17GE-5825, filed Nov. 22,1999, and entitled “Adjustable Generator Stator Slot Wedge System”).

BRIEF SUMMARY OF THE INVENTION

[0006] This invention provides an improved mechanism for tighteninggenerator stator internal slot wedges (wedges which are inboard of theend wedges), and restoring the required radial force on the winding barsin a location where loosening can occur. It also allows the tighteningprocess to be carried without the removal of the generator field.

[0007] The invention also increases the long term durability andreliability of the internal wedges by making design and materialsimprovements which also contribute to decreasing the outage frequencyfor generator inspections and down time.

[0008] In an exemplary embodiment of the invention, an adjustableversion of the restraining device commonly referred to as a stator slotwedge is provided. The principal purpose of the stator slot wedge is tosupply a radial force to the armature winding (stator bars) to preventit from vibrating under the influence of electromagnetic forces whichact continuously during normal operation and which can become much moresevere under conditions caused by misoperation or system faults.

[0009] The invention has several features which in combination yield theunique support device, the main feature of which is adjustabletightening of internal wedges in place, i.e., without removal of thegenerator field. The individual design features include: (1) an oblongslot in the wedge component that provides access for a tightening tool;(2) rounded holes in the slide component that serve as an insertlocation for a tool designed to provide proper tightening; and (3)stepped internal wedges and slides, otherwise similar to the end wedgesand slides in the above identified co-pending application, that preventreverse axial movement or loosening.

[0010] In the exemplary embodiment, wedge and slide components areprovided that are similar to those disclosed in copending applicationSer. No. ______,identified above. In accordance with this invention, anelongated or oblong slot is formed in the wedge component that providesaccess to the stepped surface on the underlying slide component. Inaddition, a series of round holes are provided in the slide component ingenerally aligned relationship with the slot, to allow the head of anadjustment tool to be inserted through the slot and into one of theholes on the slide component. By appropriately locating and then pushingthe tool inwardly, the slide component is moved inwardly in a ratchetingtype action, to tighten the internal slot wedge/slide assembly andthereby restore the required radial force on the winding bars.

[0011] Accordingly, in its broader aspects, the present inventionrelates to a generator stator including a magnetic core having aplurality of axially extending radial slots arranged about the peripherythereof with windings in each radial slot; at least one adjustableassembly axially inboard of an outermost end assembly in each radialslot, arranged to restrain the windings in the radial slot, theadjustable assembly comprising mating wedge and slide components whichinterface along stepped matching surfaces, the wedge component having anelongated slot therein providing access to the slide component.

[0012] In another aspect, the invention relates to a generator statorincluding a magnetic core having a plurality of axially extending radialslots arranged about the periphery thereof with windings in each radialslot; at least one adjustable assembly axially inboard of an outermostend assembly in each radial slot, arranged to restrain the windings inthe radial slot, the adjustable assembly comprising mating wedge andslide components which interface along stepped matching surfaces, thewedge component having an elongated slot therein providing access to theslide component; wherein a second adjustable assembly is located axiallyinboard of the at least one adjustable assembly, the second adjustableassembly comprising a second wedge component and a second slidecomponent having interengaging stepped surfaces, the second wedgecomponent having an elongated slot therein providing access to thestepped surface in the slide.

[0013] In still another aspect, the invention relates to a tool for usein adjusting an axially inboard wedge and slide assembly in a generatorstator slot wedge system, the tool comprising an elongated handle, atool head comprising an elongated handle, a tool head pivotally securedto the handle, and a stub formed on a remote end of the tool head, thestub having a substantially cylindrical shape.

[0014] Other objects and advantages of the subject invention will becomeapprent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a partial axial section view of the stator core slotwith slide and wedge components in place, so as to supply radial forcesto the armature winding or stator bar;

[0016]FIG. 2A is a partial side elevation of end wedge and slidecomponents in their initially installed condition;

[0017]FIG. 2B is a view similar to FIG. 2A but with the slide and wedgecomponents in a loosened condition;

[0018]FIG. 2C is a section similar to 2A and 2B but with a slidecomponent driven fully under the wedge component in order to correct theloosened condition shown in FIG. 2B;

[0019]FIG. 3 is a plan view of internal slide and wedge components inaccordance with the subject invention; and

[0020]FIG. 4 is a perspective view, partially cut away, illustrating atool in engagement with the internal slot and wedge components shown inFIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Referring to FIG. 1, the magnetic stator core is partially shownat 10, with a plurality of radial slots 12 extending axially along thecore stator windings 14. Each slot 12 is formed adjacent its mouth witha dovetail groove or undercut 16, permitting wedge and slide components18, 20 to be inserted in an axial direction within the slot. Prior tothe insertion of the end and inboard stepped wedge and slide assemblies,conventional wedges are inserted from the axial center of the coreoutwardly in opposite directions. The individual wedges are generallybetween about 4 and 7 inches in length, and the stator core may have alength of between about 60 and 330 inches. The two axially adjacentwedge locations (the end location and the next adjacent locationreferred to herein as an inboard or internal location) at respectiveopposite ends of the core are fitted with the wedge and slide assemblies18, 20 and 40, 42 described in greater detail below. This inventionrelates specifically to the wedge and slide components at the inboardlocation adjacent the end wedge and slide components.

[0022] With reference also to FIG. 2A, the end wedge 18 is formed with aflat top surface 22 and an inclined lower surface 24 machined to includea series of integral steps (i.e., 22 and 24 are stepped matchingsurfaces) defined by vertical shoulders 26 which connect adjacentinclined surface portions 28, with the wedge increasing in thickness inan “inward direction”, i.e., in the insertion direction toward the axialcenter of the core 10. Along the axially extending sides of the upperportion of the wedge, there are laterally extending dovetail projections30 which mate with the dovetail grooves 16 in the slot 12.

[0023] The end slide component 20 has a flat bottom surface 32 and aninclined upper surface 34 machined to include a series of steps definedby vertical shoulders 36 which connect adjacent inclined ramp portions38, with the slide decreasing in thickness in the “inward” or insertiondirection. The slide 20 is preferably a high strength laminate. Thewedge and slide components 18, 20 thus interface along matching steppedcontact planes (the inclined surface portions 28 and 38 are equal inlength and have the same slope). Surface portions 28, 38 lie at an acuteangle to the center axis of the core. It is preferred that this anglelie in the range of from about 3° to about 8°. Between the winding 14and the slide 20, there are one or more axially extending filler strips37, 39.

[0024] While the wedge and slide components shown in FIGS. 2A, 2B and 2Care end wedge and slide components, it will be understood that theinternal or inboard wedge and slide components (shown partially at 40,42) are of similar design except as noted below. It should also beunderstood that the construction and materials employed in theconstruction of the inboard slide and wedge components 40, 42 may be asdescribed in the above identified co-pending application.

[0025] During assembly, after the internal wedge and slide components40, 42 have been inserted in the usual manner, the wedge and slidecomponents 18, 20 are inserted in the slot 12, with the wedge 18inserted first, supported by the dovetail grooves 16. With the fillerstrips 37, 39 located atop the winding 14, the slide 20 is insertedaxially as shown in FIG. 2A, i.e., radially between the wedge 18 and thewindings 14. As shown there, the slide 20 is driven tight in the axialdirection to provide the required radial force on the winding bars, butwith the capability to be driven axially an additional distance L, asneeded at later dates, to eliminate radial clearances and to restoreradial wedge force.

[0026] In FIG. 2B, the end slide and wedge assembly is shown in aloosened condition where radial clearances have developed in the slot asa result of bar and wedge shrinkage and compaction over time. Of course,the stepped configuration between the slide and wedge prevents the slidefrom “backing out” of the slot even though radial clearances havedeveloped.

[0027]FIG. 2C illustrates a corrected and tightened condition where theslide 20 has been driven axially further into the slot through thedistance L, so that the forward and rearward ends of the slide and wedgelie flush with one another. It will be understood that the depiction inFIGS. 2A-2C is schematic in nature and does not reflect the exact stepsize, slope, or axial travel.

[0028] There remains a need, however, to adjust the inboard or internalwedge and slide components 40, 42 as well. Turning now to FIGS. 3 and 4,the internal wedge component 40 is formed with an elongated or oblongslot 44 that exposes the stepped surface 46 on the internal slidecomponent 42. The slot 44 is elongated, with rounded ends 48 and 50, andis located along the longitudinal axes of the wedge and slidecomponents. The wedge component 42 is formed with a matching steppedsurface 47 which engages the stepped surface 46 of the slide component.

[0029] A series of vertical (or radial) holes 52 are formed in the slidecomponent 42, aligned with the slot 44 in the wedge component 40. Theseholes 52 are adapted to receive the forward, cylindrically shaped stub54 of a tool 56 shown in FIG. 4.

[0030] The tool 56 includes an elongated handle 58 pivotally attached toa tool head 60 by means of a pivot pin 62, with the stub 54 located atthe opposite end of the tool head from the pivot pin 62. It will beappreciated that the tool head 60 and handle 58 can be “straightenedout,” i.e., axially aligned and inserted in a space between the statorand rotor. A cable (not shown) can be attached to the head 60 via hole64 and pulled to pivot the tool head 60 to the orientation shown in FIG.4. The generally cylindrical stub 54 may then be located in one of theadjustment holes 52 via slot 44, and with the forward end of the head 60in engagement with the rounded end 50 of the slot 44, the tool may bepushed forwardly to drive the slide relative to the wedge (creatingopposing forces indicated by arrows 66, 68) along the matching steppedsurfaces 46, 47 in a ratchet-like action to take up any radial clearancebetween the wedge and the stator.

[0031] Whether additional of the adjustment holes 52 are used isdependent upon the extent of the axial adjustment necessary to tightenthe wedge.

[0032] The invention has particular application in any turbine-generatorhaving high electromagnetic forces during normal operation which, inconcert with other adverse conditions, might result in severe stator bardamage. It may be installed in new machines or retrofitted to existingunits during rewedging or armature rewind operations.

[0033] While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A generator stator including a magnetic corehaving a plurality of axially extending radial slots arranged about theperiphery thereof with windings in each radial slot; at least oneadjustable assembly axially inboard of an outermost end assembly in eachradial slot, arranged to restrain said windings in said radial slot,said adjustable assembly comprising mating wedge and slide componentswhich interface along stepped matching surfaces, said wedge componenthaving an elongated slot therein providing access to said slidecomponent.
 2. The generator stator of claim 1 wherein said steppedsurface on said slide component is formed with at least one hole forreceiving a tool stub adapted to be inserted through said elongatedslot.
 3. A generator stator including a magnetic core having a pluralityof axially extending radial slots arranged about the periphery thereofwith windings in each radial slot; an adjustable end wedge assembly atthe outermost ends of each radial slot, arranged to restrain saidwindings in said radial slot, each said adjustable end wedge assemblycomprising mating end wedge and slide components which interface alongfirst stepped matching surfaces; and an adjustable inboard wedgeassembly located axially adjacent each said adjustable end wedgeassembly, each said adjustable inboard wedge assembly comprising matinginboard wedge and slide components which interface along second steppedmatching surfaces, said inboard wedge component having an elongated slottherein providing access to the stepped surface in said inboard slidecomponent.
 4. The generator stator of claim 3 wherein said steppedsurface on said inboard slide component is formed with at least one holefor receiving a tool stub adapted to be inserted through said elongatedslot.
 5. A tool for use in adjusting an axially inboard wedge and slideassembly in a generator stator slot wedge system, the tool comprising anelongated handle, a tool head pivotally secured to said handle, and astub formed on a remote end of said tool head, said stub having asubstantially cylindrical shape.
 6. The tool of claim 5 wherein saidtool head is formed with means for attaching a cable for pulling saidtool head to an angled orientation relative to said handle.